Editing IPCC:AR6/WGIII/Chapter-7 (section)

==== 7.4.3.7 Manure Management ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Manure management measures aim to mitigate CH 4 and N 2 O emissions from manure storage and deposition. Mitigation of N 2 O considers both direct and indirect (i.e., conversion of ammonia and nitrate to N 2 O) sources. According to the SRCCL, measures may include (i) anaerobic digestion, (ii) applying nitrification or urease inhibitors to stored manure or urine patches, (iii) composting, (iv) improved storage and application practices, (v) grazing practices and (vi) alteration of livestock diets to reduce nitrogen excretion ( [[#Mbow--2019|Mbow et al. 2019]] ; [[#Jia--2019|Jia et al. 2019]] ). Implementation of manure management with other livestock and soil management measures can enhance system resilience, sustainability, food security and help prevent land degradation (Smith et al. 2014; [[#Mbow--2019|Mbow et al. 2019]] ; P. [[#Smith--2019|Smith et al. 2019]] a), while potentially benefiting the localised environment, for example, regarding water quality ( [[#Di--2016|Di and Cameron 2016]] ). Risks include increased N 2 O emission from the application of manure to poorly drained or wet soils, trade-offs between N 2 O and ammonia emissions and potential eco-toxicity associated with some measures.

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The AR5 reported manure measures to have high (&gt;10%) mitigation potential. The SRCCL estimated a technical global mitigation potential between 2020 and 2050 of 0.01–0.26 GtCO 2 -eq yr –1 , with the range depending on economic and sustainable capacity ( [[#Dickie--2014a|Dickie et al. 2014a]] ; [[#Herrero--2016|Herrero et al. 2016]] ) (SRCCL, Chapter 2). Conversion of estimates to native units is restricted as a mixture of GWP100 values was used in underlying studies. Measures considered were typically more suited to confined production systems ( [[#Jia--2019|Jia et al. 2019]] ; [[#Mbow--2019|Mbow et al. 2019]] ), while improved manure management is included within IAM emission pathways ( [[#Rogelj--2018b|Rogelj et al. 2018b]] ).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Research published since SRCCL broadly focuses on measures relevant to intensive or confined systems (e.g., ( [[#Hunt--2019|Hunt et al. 2019]] ; [[#Kavanagh--2019|Kavanagh et al. 2019]] ; Sokolov et al. 2020; [[#Im--2020|Im et al. 2020]] ; [[#Adghim--2020|Adghim et al. 2020]] ; [[#Mostafa--2020|Mostafa et al. 2020]] ), highlighting co-benefits and risks. For example, measures may enhance nutrient recovery, fertiliser value ( [[#Sefeedpari--2019|Sefeedpari et al. 2019]] ; [[#Ba--2020|Ba et al. 2020]] ; [[#Yao--2020|Yao et al. 2020]] ) and secondary processes such as biogas production ( [[#Shin--2019|Shin et al. 2019]] ). However, the potential antagonistic relationship between GHG and ammonia mitigation and need for appropriate management is emphasised ( [[#Aguirre-Villegas--2019|Aguirre-Villegas et al. 2019]] ; [[#Grossi--2019|Grossi et al. 2019]] ; [[#Kupper--2020|Kupper et al. 2020]] ; [[#Ba--2020|Ba et al. 2020]] ). In some circumstances, fugitive emissions may reduce the potential mitigation benefits of biogas production ( [[#Scheutz--2019|Scheutz and Fredenslund 2019]] ; [[#Bakkaloglu--2021|Bakkaloglu et al. 2021]] ), while high implementation cost is identified as an adoption barrier, notably of anaerobic digestion ( [[#Liu--2018|Liu and Liu 2018]] ; [[#Niles--2019|Niles and Wiltshire 2019]] ; [[#Ndambi--2019|Ndambi et al. 2019]] ; [[#Ackrill--2020|Ackrill and Abdo 2020]] ; [[#Adghim--2020|Adghim et al. 2020]] ). Nitrification inhibitors have been found to be effective at reducing N 2 O emissions from pasture deposited urine (López-Aizpún et al. 2020), although the use of nitrification inhibitors is restricted in some jurisdictions due to concerns regarding residues in food products ( [[#Di--2016|Di and Cameron 2016]] ; [[#Eckard--2020|Eckard and Clark 2020]] ) while ''limited evidence'' suggests eco-toxicity risk under certain circumstances ( [[#Kösler--2019|Kösler et al. 2019]] ). Some forage crops may naturally contain inhibitory substances ( [[#Simon--2019|Simon et al. 2019]] , 2020; [[#de%20Klein--2020|de Klein et al. 2020]] ), though this warrants further research ( [[#Podolyan--2020|Podolyan et al. 2020]] ; [[#Gardiner--2020|Gardiner et al. 2020]] ).

Country specific studies provide insight into regionally applicable measures, with emphasis on small-scale anaerobic digestion (e.g., dome digesters), solid manure coverage and daily manure spreading in Asia and the Pacific, and Africa ( [[#Hasegawa--2012|Hasegawa and Matsuoka 2012]] ; [[#Hoa--2014|Hoa et al. 2014]] ; [[#Jilani--2015|Jilani et al. 2015]] ; [[#Hasegawa--2016|Hasegawa et al. 2016]] ; [[#Pradhan--2017|Pradhan et al. 2017]] ; [[#Ericksen--2018|Ericksen and Crane 2018]] ; [[#Pradhan--2019|Pradhan et al. 2019]] ; [[#Kiggundu--2019|Kiggundu et al. 2019]] ; [[#Dioha--2020|Dioha and Kumar 2020]] ). Tank/lagoon covers, large-scale anaerobic digestion, improved application timing, nitrogen inhibitor application to urine patches, soil-liquid separation, reduced livestock nitrogen intake, trailing shoe, band or injection slurry spreading and acidification are emphasised in Developed Countries ( [[#Kaparaju--2011|Kaparaju and Rintala 2011]] ; [[#Eory--2015|Eory et al. 2015]] ; Pape et al. 2016; [[#Jayasundara--2016|Jayasundara et al. 2016]] ; [[#Pellerin--2017|Pellerin et al. 2017]] ; [[#Liu--2018|Liu and Liu 2018]] ; [[#Lanigan--2018|Lanigan et al. 2018]] ; [[#Carroll--2019|Carroll and Daigneault 2019]] ; [[#Eckard--2020|Eckard and Clark 2020]] ). Using IPCC AR4 GWP100 values for CH 4 and N 2 O, a recent assessment finds 69% (63.4 MtCO 2 -eq yr –1 ) of economic potential (up to USD100 tCO 2 -eq –1 ) between 2020–2050, to be in Developed Countries ( [[#Roe--2021|Roe et al. 2021]] ).

'''Critical assessment and conclusion.''' There is ''medium confidence'' that manure management measures have a global technical potential of 0.3 (0.1–0.5) GtCO 2 -eq yr –1 , (using a range of IPCC GWP100 values for CH 4 and N 2 O), of which 0.1 (0.09–0.1) GtCO 2 -eq yr –1 is available at up to USD100 tCO 2 -eq –1 (Figure 7.11). As with other non-CO 2 GHG mitigation estimates, values may slightly differ depending upon which IPCC GWP100 values were used. There is ''robust evidence'' and ''high agreement'' that there are measures that can be applied in all regions, but greatest mitigation potential is estimated in Developed Countries in more intensive and confined production systems.

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